The proposed project will use transcleral microelectrode recording to electrophysiologically classify cat retinal ganglion cells. Following electrophysiological classification, the ganglion cell will be intracellularly injected with horseradish peroxidase and morphologically analyzed. Criteria for electrophysiological classification will include axonal conduction velocity, latency to stimulation of central projection sites and receptive field analysis. Experiments conducted over the previous grant period have demonstrated that there is considerable overlap in both the physiological and morphological characteristics of retinal ganglion cells previously supposed to have belonged to separate classes. One aim of this study is to securely and quantitatively deline the physiological and morphological classes of cat retinal ganglion cells. The data from these studies will describe structure/function correlations for retinal ganglion cells that will include morphological correlates of specific physiological types. Studies proposed will also define the relationship between the size of the excitatory receptive field and the extent of the dendritic arbor, between the sign (ON or OFF) of the receptive field center and the stratification of the dendritic branches in the inner plexiform layer, and describe the correlation between dendritic field orientation and preferred stimulus orientation. The methodology proposed for these experiments is the only direct approach available for realizing these aims. The data acquired in these studies will define the normal structure/function correlations for retinal ganglion cells in the adult cat and will provide a data base for comparison to future studies of the morphological and physiological development of the mammalian retina under normal and abnormal developmental conditions.